The present invention relates to a method and device for controlling a power steering device having a combination of a constant flow oil pump and a flow control valve.
A power steering device of this type controls a flow control valve in accordance with a vehicle speed, so that an oil flow varies widely in accordance with a given vehicle speed, thereby providing smooth steering operation. In this case, when a vehicle speed is increased, a smaller steering force is required. An oil flow rate is controlled to be decreased in accordance with an increase in vehicle speed. Therefore, a uniform and small steering force is required throughout the wide range of vehicle speeds. A flow rate of an oil supplied to a power steering unit is controlled to a predetermined value corresponding to a vehicle speed.
When a driver turns a steering wheel abruptly, a predetermined amount of oil must be supplied to the power steering unit within a short period of time. However, a sufficient amount of oil cannot be quickly supplied to the power steering unit, which requires a large steering force. The so-called steering wheel hitch phenomenon occurs wherein the driver temporarily feels heavy steering. In order to solve this problem, conventionally, a larger amount of oil than that required in correspondence with the current vehicle speed is supplied to the power steering unit. When a lower limit flow rate of oil supplied to the power steering unit is increased in this manner, a variable range of flow rates is narrowed since the upper limit is determined by a delivery rate of the oil pump. For this reason, any conventional system fails to satisfy the need for a uniform and small steering force throughout a wide range of vehicle speeds.